1. Field of the Invention
The present invention is directed to pressure to electrical signal transmitters. More specifically, the present invention is directed to a pressure to electrical signal transmitter having a pressure overload protection means for protecting the pressure sensor used in the transmitter.
2. Description of the Prior Art
Differential pressure transmitters using barrier diaphragms exposed to respective input pressures and a sensor providing an electrical signal representative of the difference in pressure between two applied input pressures are known in the art as shown in the Weaver et al U.S. Pat. No. 3,712,143. Such differential pressure transmitters include a transmitter structure which contains two barrier diaphragms. A first chamber on one side of a first diaphragm is filled with an incompressible fill fluid and a second chamber on one side of the other, or second, barrier diaphragm is filled with a second incompressible fill fluid. The other side of each of the first and second barrier diaphragms is exposed to a respective process, or input, fluid for applying input pressure thereto which may be process fluids derived from respective sides of a so-called orifice plate in a process fluid flow line. In such an application, the transmitter is arranged to produce an electrical output signal representative of differential pressure between the two input fluids. The fill fluids communicate with opposite, or respective, sides of a sensor element, e.g., a strain sensitive semi-conductor chip, which is displaced or deflected by an amount dependent on the difference between the pressures of the fill fluids which, in turn, is representative on the differential pressure of the applied input fluids. The sensor may be located within the transmitter body as shown in the aforesaid Weaver patent or externally of the transmitter body as shown in the Whitehead, Jr. U.S. Pat. No. 4,072,058. Because of the extremely small full range displacement capability of the sensor in transmitters of this type, it has been necessary to equip such transmitters with overload protection arrangements to prevent the sensors from being excessively displaced, or deflected, and, hence, either damaged or destroyed by excessive applied input fluid pressures. In the aforesaid U.S. patents, the transmitters are provided with various input pressure overload arrangements. Other input pressure overload protective structures are shown in U.S. Pat. Nos. 3,313,158; 3,400,588 and 3,841,158. Those prior art input pressure overload protection arrangements exhibit significant shortcomings in that they require an excessive amount of space within a transmitter body to be devoted to the overload protection device and fail to provide an overload protection structure which can be usable with either an externally located sensor or an internally located sensor.